1. Field of the Invention
The present invention relates generally to compositions and methods for delivering nucleic acids to the lungs of humans and other animal hosts. More particularly, the present invention relates to compositions which are formed by incorporating nucleic acid constructs within a hydrophilic excipient matrix. The resulting compositions are then stored and utilized in dry powder form.
A form of human gene therapy which is receiving increasing interest relies on the in vivo delivery of functional nucleic acids, usually structural genes, to certain target cells within a human or other host. The nucleic acids may be incorporated into carriers such as viruses, liposomes, or the like, and will be delivered under conditions which result in uptake of the genes into the target cells, with subsequent expression of the genes for an extended period of time.
Of particular interest to the present invention, it has been demonstrated that nucleic acid constructs can be delivered to the lungs of mice and rats by different routes, including intratracheal administration of a liquid suspension of the nucleic acids and inhalation of an aqueous aerosol mist produced by a liquid nebulizer. Although holding great promise, both methods for the delivery of nucleic acids to the lungs suffer from certain drawbacks. Intratracheal administration is not suitable for routine therapeutic use in humans and has a very low patient acceptability. Moreover, intratracheal instillation often results in very uneven distribution of a dispersion in the lungs, with some regions receiving very little or no material. The use of a liquid nebulizer enjoys higher patient acceptability and achieves better distribution, but requires time-consuming equipment set-up, can require prolonged periods of treatment to achieve an adequate dosage, can inactivate a viral carrier, and can result in undesirable aggregation or degradation of the nucleic acids within the aerosol mist. Aggregated nucleic acids will generally be less suitable for uptake into host target cells.
For these reasons, it would be desirable to provide improved compositions and methods for the aerosol delivery of nucleic acids. The compositions will preferably be in a dry powder form which can be readily dispersed in a flowing air stream to provide a dry aerosol for delivery to a patient. The dry powder formulations will permit delivery of required dosages of nucleic acids in a very rapid manner (typically in several or fewer breaths) and will be suitable for storage over extended periods. The dry powders are delivered to particular target regions within the host and are readily dispersed over the internal surfaces of lung, where the powder dissolves in the moist layer over the surfaces to thereby release nucleic acids to interact with the target cells.
2. Description of the Background Art
Stribling et al. (1992) J. BIOPHARM. SCI. 3:255-263, describes the aerosol delivery of plasmids carrying a chloramphenicol acetyltransferase (CAT) reporter gene to mice. The plasmids were incorporated in DOTMA or cholesterol liposomes, and aqueous suspensions of the liposomes were nebulized into a small animal aerosol delivery chamber. Mice breathing the aerosol were found to at least transiently express CAT activity in their lung cells. Rosenfeld et al. (1991) SCIENCE 252:431-434, describes the in vivo delivery of an .alpha.1-antitrypsin gene to rats, with secretion of the gene product being observable for at least one week. An adenoviral vector containing the gene was diluted in saline and instilled directly into the rat trachea. Underwood et al. (1991) J. PHARMACOL. METH. 26:203-210, describes the administration of dry powder bronchodilators in a lactose carrier to pig lungs. U.S. Pat. No. 5,049,388 describes the delivery of liquid aerosols containing liposomes to the lungs. Friedman (1989) SCIENCE 244:1275-1281 is a review article describing human gene therapy strategies. In Felgner and Ringold (1989) NATURE 387-388, it is described that the presence of certain polyvalent ions can reduce transfection efficiency in vitro using liposomes. Gershon et al. (1993) BIOCHEMISTRY 32:7143-7151 describe that multivalent anions such as citrate or phosphate can induce fusion of positively-charged liposomes used for transfection.